1. Field of the Invention
The present invention relates to a ferroelectric emitter. More specifically, the present invention relates to a ferroelectric multi-layered emitter used in a semiconductor lithography process.
2. Description of the Related Art
Ferroelectric emission by switching allows for a simple process in electron emission lithography. In the past, electron emission suitable for lithography has been obtained by switching an emitter in a magnetic field. However, a conventional ferroelectric emitter cannot guarantee electron emission where the gap between two electrodes is too wide or too narrow for switching.
For example, in the conventional ferroelectric emitter, if the gap between two electrodes is too wide an electric field cannot reach the center portion of the ferroelectric emitter. Thus a switching effect does not occur in a ferroelectric region. If, on the other hand, the gap between the two electrodes, or a gap of a mask pattern, is too narrow, then the mask pattern formed on a ferroelectric layer in a ferroelectric emitter absorbs electrons during electron emission, so that electrons flow through the patterned mask. Moreover, an isolated pattern, such as a doughnut shape, cannot be switched because the two electrodes are not connected to each other.
In contrast to ferroelectric switching, pyroelectric emission can provide a uniform emission of electrons regardless of the characteristics of a gap of a mask pattern. Pyroelectricity refers to the production of polarization changes by temperature variations. Due to such properties, when a material is subjected to a temperature change, the magnitude of a spontaneous polarization changes to affect bound charges, so that a current flows between the top and bottom electrodes.
If an emitter is heated and this process occurs in a vacuum, then bound charges, which are electrons screening on the surface of the emitter, are released in a vacuum, which is called pyroelectric emission. In this case, uniform emission is allowed regardless of a gap distance. Furthermore, pyroelectric emission enables uniform electron emission in an isolated pattern such as a doughnut pattern. Although it facilitates electron emission, pyroelectric emission has several disadvantages. One of the disadvantages is the requirement the restriction of re-poling an emitter or heating an emitter above the Curie temperature for re-emission.